The following documents are incorporated herein by reference: K. Nagaraj, H. S. Fetterman, J. Anidjar, S. H. Lewis, and R. G. Renninger, “A 250 mW 8-b 52 Msamples/s Parallel-Pipelined A/D Converter With Reduced Number of Amplifiers”, IEEE Journal of Solid State Circuits, Vol. 32, No. 3, March 1997; and P. Yu and H. S Lee, “A 2.5v, 12-b, 5-Msamples/s Pipelined CMOS ADC”, IEEE Journal of Solid Sate Circuits, Vol. 31, No. 12, March 1996.
Switched capacitors are one of the basic building blocks in analog circuitry. A switch, which couples a potential to a capacitor, closes to charge the capacitor to the potential. The switch then opens so that the charge remains on the capacitor. Switched-capacitor amplifiers are widely used in metal oxide semiconductor (MOS) integrated circuits, for example, as amplifiers or comparators in analog-to-digital or digital-to-analog converters. Typically these integrated circuits are used in low-power systems. The input and feedback portions of such switched-capacitor amplifiers are formed using capacitors rather than resistors. Because integrated capacitors are generally smaller than integrated resistors, switched-capacitor amplifiers can be fabricated more compactly than amplifier circuits based on resistors. Further, the gain of switched-capacitor amplifiers is determined by the ratio of the integrated capacitors used in the input and feedback portions of the amplifier circuit. Because the integrated capacitors can be manufactured to high tolerances, switched-capacitor amplifiers can be fabricated with accurate gains.
However, conventional switched-capacitor amplifiers exhibit a number of non-ideal characteristics which must be addressed. One such characteristic is the charge injection effect from the MOS switches. Charge injection is the charge in the channel of the transistor dissipating by leakage to the drain and/or the source of the transistor. In this case, as the switch opens (i.e., the MOS is switched off), there is a transfer of charge from the transistor to the capacitor. As accuracy requirements for circuits become more stringent, the effect of charge injection error becomes correspondingly more problematic.